Morphology and Distribution of Causative Microorganisms Involved in Anaerobic Bulking in the EGSB Reactor

摘要

The most serious problem in the operation of expanded granular sludge bed (EGSB) reactors is the anaerobic bulking caused by the overgrowth of microorganisms. Once the anaerobic bulking occurs, the EGSB reactors have to be stopped due to the outflow of granular sludge. Our previous study showed that several species belonging to the phyla Euryarchaeota, Chloroflexi. and Proteobacteria in the anaerobic bulking sludge were more abundant than those in healthy granular sludge in a mesophilic EGSB reactor that treated high-strength organic wastewater discharged from a food-manufacturing factory. Therefore, this study aimed to investigate the morphological characteristics of these microorganisms, and to clarify the spatial distribution in healthy granular sludge. 16S rRNA-targeted in situ DNA-hybridization chain reaction demonstrated that Chloroflexi bacteria and Methanosaeta archaea belonging to the phylum Euryarchaeota forms filamentous cells, strongly involving in the anaerobic bulking. Fluorescence in situ hybridization using 16S rRNA-specific DNA probes revealed that Chloroflexi bacteria were abundantly distributed in the surface part of healthy granular sludge, while Methanosaeta archaea were relatively distributed in the part of close to center. These results suggest that microorganisms having different substrate utilization might had caused the anaerobic bulking by stepwise overgrowth of each microbe.